NASA delays launch of Discovery yet again

For the third time in as many weeks, NASA pushed back the launch of space shuttle Discovery, announcing Friday night that the mission to the international space station will not take off before Feb. 27 at the earliest.

Teams of agency engineers have been wrestling with problems involving fuel valves in the shuttles' main engines. It has been clear for days that the problem was thornier than thought, and NASA wants to give engineers more time to pore over test data.

The launch originally planned for Thursday has been pushed back twice. NASA wants to make sure three valves that control the flow of hydrogen into the external fuel tank will not endanger the shuttle and its seven-man crew if they break. A small piece of one valve cracked off on the flight of Endeavour in November.

In a news release, the space agency said engineers have made "significant progress" in understanding what caused the damage to a flow control valve on Endeavour but gave no details.

The Discovery mission to install new solar wings on the space station is the first of five flights set for 2009. NASA said the new target date is not expected to affect the other missions, including STS-125 to service the Hubble Space Telescope.